BREAKING THE CONNECTION - DISPLACEMENT OF THE DESMOSOMAL PLAQUE PROTEIN DESMOPLAKIN FROM CELL-CELL INTERFACES DISRUPTS ANCHORAGE OF INTERMEDIATE FILAMENT BUNDLES AND ALTERS INTERCELLULAR JUNCTION ASSEMBLY
Ea. Bornslaeger et al., BREAKING THE CONNECTION - DISPLACEMENT OF THE DESMOSOMAL PLAQUE PROTEIN DESMOPLAKIN FROM CELL-CELL INTERFACES DISRUPTS ANCHORAGE OF INTERMEDIATE FILAMENT BUNDLES AND ALTERS INTERCELLULAR JUNCTION ASSEMBLY, The Journal of cell biology, 134(4), 1996, pp. 985-1001
The desmosomal plaque protein desmoplakin (DP), located at the junctur
e between the intermediate filament (IF) network and the cytoplasmic t
ails of the transmembrane desmosomal cadherins, has been proposed to l
ink IF to the desmosomal plaque. Consistent with this hypothesis, prev
ious studies of individual DP domains indicated that the DP COOH termi
nus associates with IF networks whereas NH2-terminal sequences govern
the association of DP with the desmosomal plaque, Nevertheless, it had
not yet been demonstrated that DP is required for attaching IF to the
desmosome, To test this proposal directly, we generated A431 cell lin
es stably expressing DP NH2-terminal polypeptides, which were expected
to compete with endogenous DP during desmosome assembly. As these pol
ypeptides lacked the COOH-terminal IF-binding domain, this competition
should result in the loss of IF anchorage if DP is required for linki
ng IF to the desmosomal plaque. In such cells, a 70-kD DP NH2-terminal
polypeptide (DP-NTP) colocalized at cell-cell interfaces with desmoso
mal proteins. As predicted, the distribution of endogenous DP was seve
rely perturbed, At cell-cell borders where endogenous DP was undetecta
ble by immunofluorescence, there was a striking absence of attached to
nofibrils (IF bundles). Furthermore, DP-NTP assembled into ultrastruct
urally identifiable junctional structures lacking associated IF bundle
s. Surprisingly, immunofluorescence and immunogold electron microscopy
indicated that adherens junction components were coassembled into the
se structures along with desmosomal components and DP-NTP. These resul
ts indicate that DP is required for anchoring IF networks to desmosome
s and furthermore suggest that the DP-IF complex is important for gove
rning the normal spatial segregation of adhesive junction components d
uring their assembly into distinct structures.